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My first post was as the OP of post #8 on this board!
But that’s not what I’m bragging about. Read through my answer and you’ll find out why I brag!
Unc Cece had it “half-right” on his Ni-Cad Battery answer recently published.
I used to manage a two-way radio shop. Now, as you can imagine, Ni-Cad batteries were very popular for the handheld radios, as you could simply recharge them instead of having to buy dry-cell or alkaline batteries. One of our biggest problems was “ni-cad memory.”
It would occur when a user would take his radio out of the charger, use it for 15-20 minutes or so, then put it back in the charger. Pretty soon the battery would have only 15-20 minutes of useful life left in it. I saw this happen more than once.
While I can not give you the “scientific” answer why this occurs, I can tell you it happens, and quite a bit. I had a Ni-Cad battery on a amatuer radio of mine, and with proper charge-discharge cycles, the battery lasted me 6 years! Not bad for a product that is designed to last 1 1/2 to 2 years!
There is one way of eliminating “memory effect” from Ni-Cad cells, and that is deliberate “overshock”, as we called it - the application of high voltage for a VERY short period of time, say 2 seconds or so. CAUTION!!! Do NOT try this unless you have a variable power supply, and TWO DVMs, one to monitor the power supply, the other the battery! This can result in explosion of the battery pack if the surge voltage is left on the pack too long!
Cece, you’re right in stating the voltage in the battery is still there underneath the “memory effect”, but aside from having a TRAINED TECHNICIAN perform the above on the battery pack, there is no way to access that stored votage underneath the memory effect.
There was a VERY informative article on Ni-Cad and Ni-MH (Nickel-Metal-Hydride) batteries in a recent issue of QST magazine, I invite you to visit the ARRL website at ww.arrl.org and do a search for Ni-Cad for the article. It explains the memory effect much better than I ever could.
Thanks and keep up the good work of informing the “unwashed masses”!
Rico
"It’s hard to be religious when certain people are not incinerated by bolts of lightning…
And looky this! I got an answer from the MASTER! And it was before he even registered as the Perfect Master! Realize this was March 1999! And he quoted me!
Cecil Adams
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Rico writes:
quote:
One of our biggest problems was “ni-cad memory.”
It would occur when a user would take his radio out of the charger, use it for 15-20 minutes or so, then put it back in the charger. Pretty soon the battery would have only 15-20 minutes of useful life left in it. I saw this happen more than once.
I think what you’re describing here is the phenomenon of “voltage depression,” which I distinguished from “memory effect.” I notice even in the technical literature there is a tendency to equate these terms, but you know me, I’m a purist.
Here’s an example of voltage depression in a nickel-metal hydride battery. You’ll notice in the chart that after repeated shallow discharges the cell drops to 1.15v prematurely. But there’s still quite a bit of charge left. NiCad batteries are more susceptible to voltage depression than NiMH, but the idea is that same. The cure is simple - subject the cell or battery to several full discharge/charge cycles. I agree with rhohm that over the long run NiMH will give you less trouble in this respect than NiCads.
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